New carbides observed by high-resolution electron microscopy in a molybdenum bicrystal containing a σ=5 symmetrical boundary

Abstract

A molybdenum σ= 5 [001](310) symmetrical tilt boundary has been examined following carburization heat treatments. The resulting structure was studied by 400 kV high-resolution electron microscopy and compared with the structure of the pure boundary. It is shown that two different morphologies and carbide structures exist. One is the standard Mo₂C hexagonal phase which precipitates at the boundary, while a tetragonal structure can also be present within the grains as well as in the boundary itself. In this latter case, the carbide represents a thin (about 1 nm) continuous layer located at the boundary plane.